A randomized phase II trial of nab-paclitaxel with or without mifepristone for advanced triple-negative breast cancer.
Authors: Nan Chen, Poornima Saha, Murtuza M. Rampurwala, Sailaja Kamaraju, Olwen Mary Hahn, Frederick Matthew Howard, Gini F. Fleming, Margarite Matossian, Jincong Q. Freeman, Theodore Karrison, Suzanne D. Conzen, Rita Nanda, Erica Michelle Stringer-Reasor
Journal: Journal of Clinical Oncology (2023)

e13103 Background: Despite recent advances, treatment (tx) of metastatic triple-negative breast cancer (TNBC) remains an important unmet clinical need. Activation of the glucocorticoid receptor (GR) initiates cell survival pathways, leading to chemotherapy resistance. Furthermore, high GR expression is a negative prognostic marker in early-stage, hormone receptor negative breast cancer. We hypothesized that GR antagonism with mifepristone (mif) prior to the administration of cytotoxic chemotherapy would improve efficacy by blocking the potent anti-apoptotic signals mediated by GR activation. Methods: We conducted a phase II, randomized, placebo-controlled, multi-center study of nab-paclitaxel (nab-pac) with or without mif in patients (pts) with locally advanced, unresectable or metastatic TNBC (NCT02788981). Prior tx with nab-pac was not allowed. Two prior chemotherapies allowed in the metastatic setting. Pts were randomized to receive nab-pac 100mg/m 2 on day 1, 8, and 15 of a 28-day cycle with mif 300mg or placebo the day prior and day of each dose of nab-pac. The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (ORR), overall survival (OS), and safety and tolerability. Results: 29 patients were enrolled from September 2017 to July 2021; 16 patients were randomized to nab-pac+placebo and 13 patients to nab-pac+mif. The mean age was 53 years (range 32-73) and 34% of pts were self-reported Black. The median PFS was 3.0 and 3.0 months (mos) in the nab-pac alone and combination arms respectively (hazard ratio [HR] 0.87, 95% CI 0.37 – 2.01, p=0.739]. ORR in the nab-pac and combination arms were 31.5% and 23%, respectively; both arms had 1 complete response (CR). Median OS with nab-pac alone was 6.0 mos and in the combination arm was 9.0 mos (HR=0.67, 95% CI 0.29 – 1.16, p=0.350]. The pt on the mif arm who achieved a CR completed 50 cycles and ultimately died of a non-cancer, non-tx related event. Tx was generally well-tolerated, with a safety profile comparable with nab-pac monotherapy. The most common treatment-related adverse events (TRAEs) were fatigue (50%), neuropathy (42%), and neutropenia (42%); the most common grade 3 TRAE was neutropenia. Grade 3 neutropenia occurred more frequently in pts receiving nab-pac+mif (69% vs 13%). Conclusions: This study did not achieve the desired statistical power due to poor accrual attributed to the COVID-19 pandemic and the approval of checkpoint inhibitors in advanced TNBC. Nonetheless, in this subset of patients, the addition of mif to nab-pac did not significantly improve PFS compared to nab-pac alone. There was a trend towards improvement in OS, primarily driven by one long-term responder. GR activation remains relevant in advanced TNBC. Further investigation of this pathway and other strategies to target chemotherapy resistance are needed. Clinical trial information: NCT02788981 .